Device for carrying out a material exchange process

Abstract

The present invention relates to an apparatus for carrying out a mass transfer process, comprising a column having at least two inlet pipes for introducing a gas phase, wherein separation active internals are housed in the column, and wherein a column section extends from the at least two inlet pipes to the separation active internals, wherein within the section the column cross-sectional area coverage is less than 25% based on the total cross-sectional area, and the at least two inlet pipes have a height offset corresponding to no more than three inlet pipe diameters, and the at least two inlet pipes are at an angle (α) between 60° and 150° to each other and are asymmetric with respect to each other. The present invention also relates to the use of the apparatus and to a method for designing the apparatus.

Description

[Technical Field]

[0001] The present invention arises from an apparatus for carrying out a mass transfer process, comprising a column having at least two inlet pipes for introducing a gas phase, the at least two inlet pipes having a height offset equal to or less than three inlet pipe diameters. [Background technology]

[0002] Columns with at least two intake pipes for introducing a gas phase for carrying out a mass transfer process are used when particularly high throughputs are to be achieved, and the columns have correspondingly large diameters. Typical column diameters are more than 2 m. The number of intake pipes depends in particular on the number of evaporators required, which may have structurally limited dimensions and different energy carriers. Usually, one intake pipe is provided for each evaporator in the column. Mass transfer processes involving at least one gas phase carried out in columns are, for example, distillation, absorption or gas scrubbing.

[0003] U.S. Patent No. 4,019,964 describes a method for controlling heat input to an evaporator in a distillation column and the use of two evaporators. Chinese Utility Model No. 203861950 also mentions the use of two evaporators.

[0004] Currently, the intake pipes for introducing the gas phase are installed essentially at the same height in the column and are usually evenly distributed around the circumference of the column, which means that in the case of two intake pipes, for example, the intake pipes are at an angle of 180° to each other.

[0005] To enhance heat and mass transfer between different phases, columns equipped with separation-active internals are typically used. Generally, such processes involve at least one gas phase and at least one liquid phase. For the purposes of the present invention, separation-active internals are internals in which at least one gas phase and at least one liquid phase are in contact with each other with a large interfacial area, enhancing mass transfer between the at least one gas phase and the at least one liquid phase. Examples of separation-active internals include trays, which may also be referred to as mass transfer plates, structured packings, or layers of packing components. An intake pipe for introducing the gas phase is typically located below the separation-active internals. When the intake pipe is located in the bottom region of the column, it is located below all of the separation-active internals provided in the column. When it is located as a side intake, the intake pipe is located between two sections with separation-active internals, which may also be referred to as horizontal subsections of the column.

[0006] The thermodynamic design of a column sets a specific separation capacity and a specific energy input to achieve a specified separation of a mixture. This directly translates into a specific ratio of gas to liquid phase in the column. Local deviations in the ratio of gas to liquid phase due to maldistribution of the gas or liquid phase over the cross-sectional area of ​​the column must be compensated for by increasing the energy input beyond the design values ​​to achieve the specified separation of the mixture.

[0007] Therefore, to obtain intensive mass transfer, the mass transfer process in the column requires a uniform distribution of the gas phase in the separating internals, and therefore a uniform distribution of the vapor flow must be achieved in the area of ​​the intake pipe where the gas phase is introduced. However, it has been found that even a uniform distribution of the intake pipes on the periphery of the column, especially in the case of two intake pipes, leads to a loss of uniformity, i.e., a less uniform flow is formed, since the individual flows collide with each other, and does not provide an optimal distribution of the vapor flow. Summary of the Invention [Problem to be solved by the invention]

[0008] It is therefore an object of the present invention to provide an apparatus for carrying out a mass transfer process, in which a more uniform distribution of the gas phase is obtained in the intake pipe region where the gas phase is introduced below the separating active internals.A further object of the present invention is to provide the use of such an apparatus in a process in which energy can be saved. [Means for solving the problem]

[0009] The object is achieved firstly by an apparatus for carrying out a mass transfer process, comprising a column and at least two, in particular exactly two, inlet pipes for introducing a gas phase, wherein the active separation internals are accommodated in the column, a column section extends from the at least two inlet pipes to the active separation internals, the coverage of the column cross section is less than 25%, preferably less than 20%, more preferably less than 10%, more preferably less than 5% of the total column cross section, the at least two inlet pipes have a height offset corresponding to no more than three inlet pipe diameters, and the at least two inlet pipes are asymmetrically spaced apart from each other at an angle α of 60° to 150°, preferably 80° to 130°, more preferably 90° to 120°, for example 95° to 115°. The column section extends in particular from the uppermost ends of the at least two inlet pipes to the lowermost inlet to the active separation internals. The tower section preferably has a section height in the range of 0 to 3 times the intake pipe diameter, more preferably in the range of 0.5 to 1.5 times the intake pipe diameter. If the at least two intake pipes have different intake pipe diameters, these figures refer to the largest intake pipe diameter. The section height is, in particular, the shortest distance between the separation active internals and one of the at least two intake pipes. The coverage of the entire cross-sectional area of ​​the tower section is preferably less than 25%, more preferably less than 20%, more preferably less than 10%, and even more preferably less than 5% of the total cross-sectional area of ​​the tower. In particular, the cross-sectional area of ​​the tower is free between the at least two intake pipes and the separation active internals, which may also be referred to as uncovered. The tower section is preferably a closed space, free in any case from separation active internals and other internals that could represent the cross-sectional area coverage, so that an unhindered and spatially uniformly distributed flow from the at least two intake pipes can be established before the inlet to the separation active internals.Internals that may result in a coverage of more than 25% and thereby impede flow from the at least two intake pipes to the separation-active internals are, for example, horizontal internals, such as at least one tray, e.g., a collecting tray or plate, e.g., a perforated plate, and / or vertical internals, such as at least one pipe, in particular with or without a covering cap, e.g., a chimney, which usually prevents contact between the liquid phase and the gas phase, e.g., on the collecting tray. Furthermore, the column is particularly a column without a dividing wall. Any fastening devices that may be present for the separation-active internals, such as support grids that serve in particular to secure the packing or packing components in the column, or supports for stabilizing the trays and flow channels of the separation-active trays, in particular the downcomer, are considered to be part of the separation-active internals.

[0010] For the purposes of the present invention, the term "asymmetric" means unequal, e.g., asymmetric placement of the intake pipes on different circumferential portions. The asymmetry preferably includes or is provided by at least two intake pipes having different intake pipe diameters and / or an asymmetric distribution of the intake pipes on the periphery of the tower. Asymmetric distribution on the periphery can also be described as at least two intake pipes being unevenly distributed on the periphery of the tower.

[0011] The intake pipe diameters of the at least two intake pipes preferably differ by at least 10%, more preferably at least 20%, in particular at least 25% based on the smallest intake pipe diameter, in particular the average intake pipe diameter of the intake pipes at the inlet to the tower.

[0012] The angle α preferably differs from the other angle β between the at least two intake pipes by at least 10°, more preferably by at least 30°, and even more preferably by at least 60°. In the case of exactly two intake pipes, the angle α preferably differs from the other angle β between the two intake pipes by at least 120°, more preferably by at least 180°. The angle α and the other angle β are in particular angles between two adjacent intake pipes. The angle α is preferably the smallest angle between the two intake pipes.

[0013] Furthermore, the asymmetry can include or be provided by different average flow velocities through the at least two intake pipes. The average velocities in the at least two intake pipes preferably differ by at least 10%, more preferably at least 30%, and in particular at least 45% relative to the lowest velocity. To determine the average velocity, for example, it is possible to carry out flow measurements, especially in the case of a pure gas supply stream. In the case of an evaporator, the amount of water vapor used to heat the evaporating medium can be used, for example, as a proportional measure of the amount of steam flowing through the intake pipes.

[0014] In the case of three or more intake pipes, the intake pipes may preferably be at various angles to one another. Therefore, in this case, the three or more intake pipes are distributed asymmetrically on the circumference of the tower. For measuring the height offset, the midpoint of the cross section of each intake pipe is preferably used as a reference.

[0015] At least two intake pipes allow the introduction of a larger amount of gas phase than would be possible if only one intake pipe were used. In particular, for the same amount of gas phase, the gas phase can be introduced at a slower speed, which results in a lower collision energy of the introduced gas phase streams and a more uniform flow distribution.

[0016] As a result of the more uniform flow distribution, energy may be saved in the mass transfer process in which the apparatus is used because local non-uniformities in the liquid to gas phase ratio are reduced or avoided.

[0017] The axial component of the velocity of the gas phase at the inlet to the separating active internals of the column is used as a measure of uniform flow distribution. For this purpose, the difference between the velocity magnitude at which the velocity is high over only 5% of the cross-sectional area and the velocity magnitude at which the velocity is low over only 5% of the cross-sectional area is calculated. The smaller this difference is, relative to the average velocity, the more uniform the flow distribution.

[0018] Surprisingly, it has been found that, unlike the case of uniform or symmetrical distribution of at least two intake pipes around the outer periphery of the column, a more uniform flow distribution can be achieved when using an arrangement of the intake pipes in which the at least two intake pipes are at angles and asymmetry between them ranging from 60° to 150°. In particular, this arrangement of at least two intake pipes makes it unnecessary to convey and / or guide the gas phase entering the column under the separation active internals through other means, such as additional internals. This is because, as a result of the collision of the targeted flows from the at least two intake pipes, i.e., from the intake pipes at corresponding angles, a flow field that is uniform in terms of flow velocity already enters the separation active internals. In the case of three or more intake pipes, the arrangement is preferably such that the three or more intake pipes are in each case at different angles to each other in order to obtain a more uniform flow distribution of the gas phase.

[0019] The mass transfer process that can be carried out using the device of the present invention is any mass transfer process involving at least one liquid phase and at least one gas phase. For the purposes of the present invention, the expression gas phase also includes boiling phases, i.e., phases containing a liquid portion and a gas portion. Conventional mass transfer processes are, for example, absorption, distillation, rectification, extraction or gas scrubbing.

[0020] In order to keep the tower construction height as low as possible, in a preferred embodiment, at least two intake pipes are arranged at the same height of the tower. In this specification, the same height means that the middle of the at least two intake pipes is at the same height, although deviations within manufacturing tolerances may occur. The arrangement of the at least two intake pipes at the same height has the additional advantage that, when the gas phase is introduced through the at least two intake pipes, and in particular the pressure and temperature are the same in all intake pipes, deviations in the physical properties of the gas phase do not occur due to the height of the at least two intake pipes.

[0021] The at least two intake pipes into which the gas phase is introduced are usually located at the bottom of the column or as side intakes of the column. When the at least two intake pipes are located as side intakes, the term "separation-active internals" in the context of the present invention refers to separation-active internals located next to and above the at least two intake pipes. In a two-phase mass transfer process, the liquid phase usually flows downward from the top of the column, while the gas phase flows upward from the bottom of the column. For this reason, the liquid phase is introduced at the top of the column, and the gas phase is introduced at the bottom and / or via a side intake. When the gas phase is the boiling phase, introduction via a side intake is particularly preferred. Subsequently, phase separation occurs in the column, with the gas portion of the boiling phase flowing upward and the liquid portion flowing downward. Of course, it is also possible to introduce the boiling phase in the bottom region of the column. In this case, the gas portion flows upward, and the liquid portion collects in the bottom region and is removed from the column via a bottom outlet.

[0022] To enhance mass transfer within the column, separation-active internals are housed within the column, preferably selected from the group consisting of trays, such as dual-flow trays, cascade trays, ripple trays, and cross-flow trays, as well as structured and random packings, and combinations thereof. The separation-active internals provide continuous separation and redistribution of the liquid and gas phases, which in turn significantly increases the interphase area, resulting in a significantly larger interphase area across which mass transfer occurs.

[0023] In the case of trays, a distinction is usually made between trays in which the liquid phase flow is directed, such as cross-flow trays, and trays in which the flow is not directed. In one embodiment, the separation-active internals preferably comprise trays in which the flow is not directed, such as dual-flow trays, ripple trays, and / or cascade trays. In another embodiment, the separation-active internals comprise cross-flow trays. More preferably, the separation-active internals comprise only trays, in particular trays in which the flow is not directed, such as dual-flow trays, ripple trays, and / or cascade trays. The flow-directed trays have at least one downcomer for the liquid, through which the liquid phase flows down onto the tray located below. In this specification, a downcomer simultaneously acts as a feed conduit to the tray located below it. The downcomers of the upper trays may be arranged in opposite positions.

[0024] Dual flow trays, ripple trays, and cascade trays are trays that do not allow the liquid phase to flow. Ripple trays are also called corrugated sieve trays. The liquid phase flows through the openings in the tray onto the tray below, and the gas phase flows from below through the openings on the tray. In this specification, it is possible that only the gas phase, only the liquid phase, both the gas and liquid phases, or neither phase flows through the openings. To allow the liquid phase to flow down from the tray, the openings of the dual flow tray do not have a chimney. Mass transfer columns with dual flow trays are described, for example, in WO 03 / 043712 or WO 2004 / 063138.

[0025] The packing used may be structured or random packing. The random packing may be, for example, a layer of packing components, and all conventional packing components known to those skilled in the art may be used as the packing components. Suitable packing components are, for example, rings, meshers, spirals, and / or saddles, such as Raschig rings, IMTP® or Pall rings, Burl saddles, or Intalox saddles, or braids. Packings having various geometric shapes, such as sheet metal packings or metal mesh packings, can be used as structured packings. In one embodiment, the separation-active internal structure preferably comprises structured packing and / or layers of packing components, and more preferably comprises only structured packing and / or layers of packing components.

[0026] Preferably, the separation active internals are made from materials including metal, ceramic, glass, carbon, graphite, polymer, or mixtures thereof. More preferably, the separation active internals consist of metal, ceramic, glass, carbon, graphite, polymer, or mixtures thereof.

[0027] The effectiveness of the separation active internals in the apparatus for carrying out the mass transfer process should preferably correspond to at least 2 theoretical plates, for example 2 to 40 theoretical plates. Separation performance is particularly preferred to be 10 to 30 theoretical plates.

[0028] When at least two inlet pipes are arranged as side inlets of the column, they are usually arranged between two trays, or when the separation active internals include structured or random packing, the inlet pipes are arranged between two segments with separation active internals, so that the gas phase can be introduced below the trays or packing and flow uniformly through the trays from below or into the packing.

[0029] When the at least two intake pipes are arranged as side intakes and in the tower bottom region, the at least two intake pipes are preferably arranged a short distance below the separation active internals, this distance corresponding to the section height. The intake pipe diameters of the at least two intake pipes preferably differ by no more than 3 times, more preferably by 1.5 times, based on the smallest intake pipe diameter. The at least two intake pipes may have the same intake pipe diameter. Furthermore, the ratio of the intake pipe diameter to the tower diameter is preferably no more than 0.8. If the at least two intake pipes have different intake pipe diameters, these figures relate to the largest intake pipe diameter.

[0030] In a preferred embodiment, the mass transfer process carried out in the column is distillation or rectification, and the column is a distillation column or rectification column. In this case, the evaporator is preferably attached to the column via at least two intake pipes for introducing the gas phase. More preferably, in each case, exactly one evaporator is attached to the column per intake pipe. A liquid is introduced into the evaporator, where it is partially or preferably completely vaporized, and the vapor is introduced into the column as a gas phase via the intake pipe. The liquid can be fed to the evaporator from the outside, or the liquid phase can be withdrawn from the column and introduced into the evaporator. Another possibility is that part of the liquid vaporized in the evaporator is fed from the outside and part is withdrawn from the column. The liquid phase withdrawn from the column and fed to the evaporator can be withdrawn, for example, at the bottom of the column. When the evaporator is used as an intermediate evaporator, the liquid phase is preferably withdrawn from the column via a side outlet, for example, a tray, and fed to the evaporator.

[0031] Another possibility is that one evaporator is used to vaporize the liquid introduced from the outside and the second evaporator is used to vaporize the liquid phase withdrawn from the column, although in this case it is preferable to feed each evaporator with the liquid introduced from the outside and the liquid phase withdrawn from the column either mixed before being introduced into the evaporator, or the liquids are introduced into the evaporator via separate conduits and mixed in the evaporator.

[0032] The evaporator can be any type known to those skilled in the art that is suitable for mass transfer processes, in particular distillation or rectification. Suitable evaporators are, for example, shell-and-tube evaporators and plate evaporators. The evaporator can be configured as a falling film evaporator, a forced draft evaporator, a forced draft expansion evaporator, a helical tube evaporator, a kettle evaporator, or a natural convection evaporator.

[0033] In a preferred embodiment of the present invention, at least two inlet pipes open radially into the column. This should be understood in particular as meaning that the extension of the central axis of the at least two inlet pipes intersects the central axis of the column. The inlet pipes can terminate at the column wall or extend into the column, but it is preferred that the inlet pipes terminate at the column wall. As a result of such measures as arranging the at least two inlet pipes at different angles α or β relative to each other and / or having different inlet pipe diameters or flow velocities, the supplied steam streams do not collide with each other symmetrically. This results in a more uniform steam flow within the column and prevents steam from concentrating midway through the column.

[0034] As an alternative to a radial arrangement, the at least two intake pipes may open into the tower at an opening angle in the radial direction.

[0035] The at least two intake pipes into which the gas phase is introduced may have any cross-sectional shape. However, it is preferable that the at least two intake pipes have a circular or elliptical cross-section. The cross-sectional area of ​​the at least two intake pipes depends on the amount of gas phase to be introduced. The cross-sectional areas of the at least two intake pipes arranged at essentially the same height can be essentially the same. In this specification, "essentially the same" means that the size of the cross-sectional area may differ as a result of manufacturing tolerances. It is also preferable that the cross-sectional shapes of the at least two intake pipes arranged at essentially the same height are the same.

[0036] Alternatively, it is of course possible for at least two intake pipes arranged at essentially the same height to have different cross-sectional areas and / or cross-sectional shapes. Different cross-sectional shapes allow local construction conditions to be taken into account. For example, in the case of heat integration, different cross-sectional areas serve to adapt the evaporator to different energy sources with different energy contents. In heat integration, part of the heat required from other heat sources is directly extracted from the process. Since the amount of heat available from the integration and the remaining amount of heat required can differ significantly, the intake pipes here have different cross-sectional areas. Furthermore, the cross-sectional area can be selected as a function of the volume of the steam flow to be supplied.

[0037] In order to find the best orientation of the at least two intake pipes relative to each other, the arrangement of the at least two intake pipes is advantageously calculated by means of a mathematical simulation. A method suitable for this purpose comprises the following steps: (a) determining the location and orientation of at least two intake pipes on a tower; (b) calculating gas flow in the column using flow simulation; (c) repeating steps (a) and (b) using different positions and orientations of at least two intake pipes; (d) selecting a position and orientation of at least two intake pipes in the flow that exhibits the most uniform flow pattern.

[0038] Any simulation program known to those skilled in the art can be used for the flow simulation. Numerical simulations based on finite elements or finite volumes, preferably based on finite volumes, are particularly suitable herein. A suitable simulation program is, for example, the commercially available ANSYS Fluent®, which operates on a finite volume basis. The flow simulation can be used to visually show the flow in the tower, and based on the results, the positions of the at least two intake pipes relative to each other can be optimized. If the at least two intake pipes have different cross-sectional shapes and / or cross-sectional areas, the optimal dimensions and shapes of the cross-sectional areas of the at least two intake pipes, which result in the most uniform flow distribution in the tower, can also be determined using the flow simulation.

[0039] Furthermore, the use of the apparatus for carrying out a mass transfer process for the production, especially for the continuous production, of isocyanates, styrene or alkyl acrylates, especially butyl acrylate, or in cracking units, especially for the dissociation of C3 hydrocarbons, has been proposed. The use of the apparatus for carrying out a mass transfer process for the continuous production of alkyl acrylates is particularly advantageous, since the process is characterized by a high energy consumption.

[0040] The apparatus for carrying out a mass transfer process is advantageously used in a process for the continuous production of butyl acrylate H2C=CH-C(=O)OR, where R=n-butyl or isobutyl.

[0041] Alkyl acrylates can be produced from 3-hydroxypropionic acid, for example, as described in WO 2019 / 034577. Alternatively, acrylic acid can be used to produce butyl acrylate.

[0042] In a first step, 3-hydroxypropionic acid can be esterified with an alcohol, followed by dehydration of the resulting 3-hydroxypropionic acid ester in a subsequent step to give the corresponding alkyl acrylate. Alternatively, in a first step, 3-hydroxypropionic acid can be dehydrated, followed by esterification of the resulting acrylic acid with an alcohol in a subsequent step.

[0043] In a process for the continuous production of butyl acrylate (HC=CH-C(=O)OR, where R=n-butyl or isobutyl), aqueous 3-hydroxypropionic acid is preferably reacted in the presence of the alcohol n-butanol.

[0044] The apparatus for carrying out the mass transfer process according to the invention is also preferably used as a rectification column in a process for the continuous production of alkyl acrylates (HC=CH-C(=O)OR, where R=n-butyl or isobutyl). Aqueous 3-hydroxypropionic acid is reacted in the presence of a suitable butanol (R-OH) under dehydration and esterification conditions in a reactor comprising a rectification column, and the butyl acrylate formed, unreacted butanol, and water used and formed are distilled at the top of the column as a ternary azeotrope. After separation into a liquid aqueous phase and a liquid organic phase, respectively, the aqueous phase and the organic phase are at least partially discharged, and the organic phase containing butyl acrylate and butanol is fractionally distilled.

[0045] Substantially acetate-free butyl acrylate can be produced using 3-hydroxypropionic acid. As used herein, "acetate" refers to n-butyl acetate or isobutyl acetate [HC-C(=O)-OR].

[0046] The 3-hydroxypropionic acid used is preferably bio-derived 3-hydroxypropionic acid. For the purposes of the present invention, "bio-derived 3-hydroxypropionic acid" refers to 3-hydroxypropionic acid produced from renewable raw materials. Furthermore, the bio-derived 3-hydroxypropionic acid is preferably produced by fermentation, particularly from glucose, xylose, arabinose, sucrose, fructose, cellulose, glucose oligomers, and / or glycerol, particularly by fermentation with subsequent purification. For example, the production of bio-derived 3-hydroxypropionic acid, also referred to as bio-3-hydroxypropionic acid or bio-HPS, by fermentation from sugars, such as glucose, and subsequent purification is known from WO 2012 / 074818.

[0047] The aqueous bio-3-hydroxypropionic acid thus produced may comprise, for example, water and essentially the following components: 35 to 70% by weight of 3-hydroxypropionic acid, 0 to 20% by weight of 3-hydroxypropionic acid oligomer, 0 to 10% by weight of acrylic acid, 0 to 1 wt. % of an acrylic acid oligomer; 0.01 to 0.1% by weight of glycolic acid, 0.01 to 0.1% by weight of 2-hydroxypropionic acid, 0.005 to 0.05% by weight of formic acid, 0 to 0.15% by weight, in particular 0.0 to 0.05% by weight, for example 0.005 to 0.10% by weight, of acetic acid, 0.005 to 0.05% by weight of succinic acid, 0.005 to 0.05% by weight of fumaric acid, 0.0001 to 0.01% by weight of formaldehyde, 0.0001 to 0.01% by weight of acetaldehyde, 0.0001 to 0.01 wt. % methanol, and Contains 0.0001 to 0.01% by weight of ethanol.

[0048] The molar ratio of butanol used to 3-hydroxypropionic acid used is preferably at least 1 and preferably less than 5. The molar ratio of butanol used to 3-hydroxypropionic acid used is particularly advantageously in the range from 1:1 to 3:1. A molar use ratio in the range from 1.1:1 to 1.8:1 is very particularly preferred.

[0049] The conditions for dehydration and simultaneous esterification are preferably provided by the presence of a catalytically active amount of acid. The content of catalytically active acid in the reactor is advantageously 0.1% to 20% by weight, more preferably 5% to 15% by weight, and in particular 7% to 10% by weight, based on the reaction mixture present therein. Preferred acids are inorganic acids, such as sulfuric acid and phosphoric acid, but also organic sulfonic acids. Among the organic sulfonic acids, methanesulfonic acid, benzenesulfonic acid, dodecylbenzenesulfonic acid, and / or p-toluenesulfonic acid are preferred. In both cases, it is also possible to use mixtures of at least one organic sulfonic acid and an inorganic acid, such as sulfuric acid. It is particularly preferred to use sulfuric acid and / or organic sulfonic acid(s) as catalyst(s) for esterification and dehydration.

[0050] The reaction of the reactants, i.e., the starting materials 3-hydroxypropionic acid and butanol in the reactor is preferably carried out at a temperature in the range of 80°C to 170°C, more preferably in the range of 100°C to 155°C, and even more preferably in the range of 120°C to 140°C. The residence time of the reactants, i.e., the starting materials 3-hydroxypropionic acid and butanol in the reactor is preferably 1 hour to 20 hours, more preferably 2 hours to 8 hours. For the purposes of the present invention, the residence time is the time during which the amount to be removed at the bottom of the reactor is present in the liquid volume of the reactor.

[0051] In the simplest case, the rectification column is placed directly on top of the reactor, from which vapor, i.e., the gas phase, rises and is usually conveyed countercurrently to the runback, i.e., the liquid phase, and fed to the rectification column. Directly superimposed rectification columns offer the advantage of conveying the vapors rising in the reactor directly to the rectification column without additional piping, and of conveying the liquid phase flowing down in the rectification column directly into the reactor.

[0052] Alternatively, the reactor and rectification column can be located separately, with appropriate piping for feeding the vapor phase to the rectification column and for discharging the liquid phase flowing through the rectification column into the reactor. Such embodiments with indirectly superimposed columns are also encompassed by the term "reactor with rectification column."

[0053] The pressure at the top of the rectification column is preferably in the range of 0.2 bar to 5.0 bar, more preferably in the range of 0.3 bar to 3.0 bar, and especially in the range of 0.5 bar to 1.2 bar.

[0054] The separation into aqueous and organic phases is preferably carried out by a phase separator. In such an apparatus, two liquids that are not uniformly miscible with each other can be separated by utilizing the difference in their densities. The resulting aqueous phase, which contains water together with butanol and, optionally, traces of other components, is preferably at least partially discharged. It is particularly preferred to discharge 10% to 80% by weight, especially 20% to 70% by weight, of the resulting aqueous phase. The remainder is preferably recycled to the rectification column in each case. A portion of the resulting organic phase is also preferably recycled to the rectification column, preferably likewise. It is preferred to recycle 0% to 80% by weight, for example, 1% to 75% by weight, more preferably 5% to 50% by weight, of the organic phase, preferably to the rectification column. The remaining portion is preferably discharged and sent to fractional distillation.

[0055] The fractional distillation of the discharged organic phase containing butyl acrylate and butanol is preferably carried out in such a way that the butanol is separated from the overhead distillate in a downstream rectification column, as described, for example, in EP-A-765859. The apparatus for carrying out the mass transfer process of the present invention can be used for the fractional distillation of the discharged organic phase. The column provided in the apparatus for carrying out the mass transfer process of the present invention can be used as the downstream rectification column. The butanol thus separated is preferably recycled to the reactor. Recycling is advantageously carried out continuously, with or without an intermediate vessel.

[0056] The fractional distillation of the organic phase comprising butyl acrylate and butanol is preferably carried out in such a way that in an additional rectification column butanol is distilled and in another additional rectification column butyl acrylate is distilled from the resulting bottoms.

[0057] The bottoms obtained from the further fractionation column consist essentially of butyl acrylate and small amounts of high boiling substances and the stabilizers used, which may also be referred to as process stabilizers, for example comprising or consisting of phenothiazine (PTZ).

[0058] In the subsequent downstream rectification column, butyl acrylate is usually separated at the top of the column. The apparatus for carrying out the mass transfer process of the present invention can be used to separate butyl acrylate. The column included in the apparatus for carrying out the mass transfer process of the present invention can be used as another downstream rectification column. During condensation, a stabilizer, particularly a storage stabilizer such as p-methoxyphenol (MeHQ), is preferably added. The bottom liquid from this subsequent downstream rectification column, which contains relatively high-boiling by-products, is advantageously recycled to the reactor, preferably continuously, with or without an intermediate vessel.

[0059] A specific embodiment involves removing butyl acrylate from the downstream fractionator to recover butanol via a side outlet after removing any incoming droplets, and condensing it to obtain the pure ester. A stabilizer, particularly a storage stabilizer such as MeHQ, is added to the ester during condensation. In this variant, the bottom liquid from the downstream fractionator essentially consists of butyl acrylate, which is preferably returned to the reactor. Particularly advantageously, the butanol obtained after separation is at least partially recycled to the reaction in the reactor. It is preferred to recycle 5% to 100% by weight of the butanol, more preferably 80% to 100% by weight.

[0060] n-Butyl acrylate can be produced by a process for the continuous production of butyl acrylate HC=CH-C(=O)OR, where R=n-butyl, in particular with a purity of ≥99.0 wt.%, more preferably ≥99.5 wt.%, with an n-butyl acetate content of ≤1000 ppm, especially ≤100 ppm. In particular, the acrylic acid content is <100 ppm, for example 5-80 ppm.

[0061] Isobutyl acrylate can be produced by a process for the continuous production of butyl acrylate HC=CH-C(=O)OR, where R=isobutyl, in particular with a purity of ≥99.0% by weight, especially ≥99.5% by weight, with an isobutyl acetate content of ≤1000 ppm, especially ≤100 ppm. In particular, the acrylic acid content is <100 ppm, for example 5-80 ppm.

[0062] In a process for the continuous production of butyl acrylate HC=CH-C(=O)OR, where R=n-butyl or isobutyl, the butyl acrylate formed is preferably stabilized with a suitable polymerization inhibitor to avoid undesired polymerization. The process is preferably carried out in the presence of an effective amount of a stabilizer or stabilizers. Suitable stabilizers are in principle all polymerization inhibitors recommended, for example, in DE-A-102005053982 and DE-A-10258329 for stabilizing acrylic acid and acrylic acid esters.Suitable stabilizers are, for example, N-oxides (nitroxyl or N-oxyl free radicals, i.e. compounds having at least one NO group), such as 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl (4HT) or 4-oxo-2,2,6,6-tetramethylpiperidine-N-oxyl, phenols and naphthols, such as p-methoxyphenol, p-aminophenol, p-nitrosophenol, 2-tert-butylphenol, 4-tert-butylphenol, 2,4-di-tert-butylphenol, Phenol, 2-methyl-4-tert-butylphenol, 2,6-tert-butyl-4-methylphenol or 4-tert-butyl-2,6-dimethylphenol, quinones such as hydroquinone or hydroquinone monomethyl ether, aromatic amines such as N,N-diphenylamine, phenylenediamines such as N,N'-dialkyl-p-phenylenediamines, in which the alkyl groups may be the same or different and independently have 1 to 4 carbon atoms and may be linear or branched, for example N, N'-dimethyl-p-phenylenediamine or N,N'-diethyl-p-phenylenediamine, hydroxylamines such as N,N-diethylhydroxylamine, imines such as methylethylimine or methylene violet, sulfonamides such as N-methyl-4-toluenesulfonamide or N-tert-butyl-4-toluenesulfonamide, oximes such as aldoximes, ketoximes or amidoximes such as diethylketoxime, methylethylketoxime or salicylaldoxime, phosphorus-containing compounds such as For example, triphenylphosphine, triphenyl phosphite or triethyl phosphite, sulfur-containing compounds such as diphenyl sulfide or phenothiazine, metal salts such as cerium(III) acetate or cerium(III) ethylhexanoate, various copper salts such as copper(II) dialkyldithiocarbamates, for example copper(II) dibutyldithiocarbamate, and also copper(II) oxinate (oxine = 4-hydroxyquinoline), and manganese salts such as manganese(II) diacetate, or mixtures thereof.Stabilization is preferably carried out using phenothiazine (PTZ), MeHQ, hydroquinone, hydroquinone monomethyl ether, 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl, 4-oxo-2,2,6,6-tetramethylpiperidine-N-oxyl, 2,6-tert-butyl-4-methylphenol or mixtures thereof. It is very particularly preferred to use phenothiazine (PTZ) and / or MeHQ and / or 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl (4HT) as polymerization inhibitors.

[0063] Even if the inhibitor can be added as a pure substance, it is advantageous to add the inhibitor dissolved in a solvent to form a solution that can be easily and reproducibly prepared, and in principle, a mixture of inhibitors in a single solution is also possible. Liquids present in any case in the acrylate synthesis process or present in the mixture in the distillation column are preferably used as solvents. Particularly preferred choices for the solvent are the acrylate product (i.e., butyl acrylate) itself, water, or one of the starting materials for the acrylate synthesis (e.g., butanol).

[0064] In particular at the lower end of the rectification column, the liquid flowing down in the rectification column, i.e. the liquid phase, is preferably at least partially removed from the rectification column, at least partially vaporized in at least one evaporator, preferably at least two evaporators, for example exactly two evaporators, and at least partially recycled to the rectification column via at least two intake pipes.

[0065] The process for the continuous production of butyl acrylate HC=CH-C(=O)OR, where R=n-butyl or isobutyl, is advantageously carried out by using specific means for controlling certain parameters. This process control is preferably carried out as follows:

[0066] For the production of butyl acrylate herein, i.e., a product with high purity, particularly greater than 99% by weight, the separation of acrylic acid from butyl acrylate in a rectification column is crucial. It has been found advantageous to set a defined ratio between the organic and aqueous runback flows. This reflux ratio of the streams is preferably in the range of 0.1 to 1.0.

[0067] Furthermore, the reaction volume at the bottom of the rectification column, or a stand-alone reactor with an indirect rectification column above it, which determines the conversion, is preferably kept constant or substantially constant. For the purposes of the present invention, substantially constant means that there is a deviation of up to ±10% by volume. This can be achieved first by a constant or substantially constant liquid flow being discharged from the reaction volume in the reactor at a constant or substantially constant liquid level. Furthermore, the volume withdrawn at the bottom preferably has a specific ratio to the inlet volume, preferably in the range of 0.01 to 0.30.

[0068] The second measure is the quality control of the acrylic acid content in the organic distillate. Since the liquid volume in the reaction space reacts rapidly with the amount of aqueous runback, the liquid level in the reactor is preferably controlled by the amount of runback, which corresponds to the amount of aqueous phase recycled.

[0069] The aqueous runback ensures that the high boiling materials n-butyl acrylate and isobutyl acrylate and the corresponding butanol can be distilled off to form a low boiling azeotrope, while the organic runback ensures that the concentration of acrylic acid formed in the reactor is maintained, particularly at a concentration below 100 ppm.

[0070] Controlling the amount of organic runback allows combining several effects, such as distillative purification, increased residence time in the reaction space, increased butanol concentration in the reaction space, etc. This control strategy results in particularly stable operation of the reactor and rectification column.

[0071] As a result of the improved control concept, butyl acrylate of improved quality, in particular improved purity, can be produced in even higher yields with lower energy consumption.

[0072] In a preferred embodiment, at least one first stabilizer is present in the rectification column, and this stabilizer is dissolved in both the aqueous phase and the organic phase in an active ratio. Such a stabilizer, such as 4HT in particular, is introduced into the rectification column above the top theoretical plate. In this way, the entire rectification column is stabilized by the stabilizer.

[0073] In addition, at least one other stabilizer, dissolved in effective proportions in both the aqueous and organic phases, is preferably introduced in the phase separator recovering the condensate and / or in the conduit of the quenching circuit and / or at the top of the condenser, and this other stabilizer is preferably the same as the first stabilizer, in particular 4HT.

[0074] The preferably provided quenching circuit (i.e. a liquid return flow of a portion of the condensate, e.g. 10 to 50 parts by weight out of 100 parts by weight of condensate to the condenser) has the function of stabilizing the vapor, which does not originally contain stabilizers, particularly appropriately during condensation in the condenser.

[0075] The amount of effective stabilizer present in solution in each phase is in particular a total amount of ≧10 ppm by weight, for example in the range of 10 to 1000 ppm by weight.

[0076] If the stabilizer used is not completely dissolved in each liquid phase, the stabilizer will accordingly exist in a suspended state.When the stabilizer exists as a suspension in a liquid phase or multiple liquid phases, this fine stabilizer fragment is practically inactive or inactive, but can provide advantages due to its function as a stabilizer storage material.For example, if the dissolved stabilizer is chemically decomposed, it will weaken the effectiveness of the stabilizer, but the active stabilizer will be newly dissolved from the suspended fragment into the solution, and if there is an appropriate intimate contact between the liquid phases, it may even occur between the phases, and may be affected by the particle size distribution of the particles.

[0077] The stabilizers can in each case be used as solutions in particularly suitable solvents, in particular as indicated above, for example the alcohols used in the process, namely butanol, water, the corresponding butyl acrylate, for example in concentrations of 1 to 5% by weight, in each case relative to the weight of the solution.

[0078] A second stabilizer, in particular PTZ, which is suitable for relatively high temperatures, and a third stabilizer, in particular MeHQ, which, due to its relatively high vapor pressure, also stabilizes the transition region between the reaction space and the lower part of the column, are advantageously introduced into the reactor. The second and third stabilizers can in each case be used as solutions in particularly suitable solvents, in particular, as indicated above, for example in butyl acrylate, which is suitably formed in the process, or in the starting material 3-hydroxypropionic acid, or in the butanol used.

[0079] An oxygen-containing gas is further advantageously used to inhibit the polymerization. For example, an air / nitrogen mixture having an oxygen content of 4% to 9% by volume is particularly suitable for this purpose. When an oxygen-containing gas is used to inhibit the polymerization, the oxygen-containing gas is preferably introduced at the bottom of the evaporator or the bottom of the reactor.

[0080] The start-up of a process for the continuous production of butyl acrylate (HC=CH-C(=O)OR, where R=n-butyl or isobutyl), which involves a reaction in a reactor and distillation in a rectification column, can be problematic, especially since changes in the runback rates of the various streams have a significant effect on the entire system. Changes in the aqueous runback rate have a relatively fast effect on the amount of vapor formed, while changes in the organic runback rate have a relatively slow effect on the acrylic acid concentration at the top of the column. However, the two runback rates are not independent of each other. When the precise runback rates do not match each other well, evaporation can be interrupted or the rectification column can flood with excessively large amounts of vapor. In that case, it is extremely difficult to restore the system to normal operating conditions.

[0081] For this reason, the reactor is advantageously first charged with an appropriate amount of a suitable reaction mixture containing butyl acrylate, particularly the bottoms product from a previous production strategy, or a suitable butyl acrylate for start-up. The bottoms are then heated to the operating temperature, i.e., the reaction temperature, and the feed streams of 3-hydroxypropionic acid, butanol, and catalyst are started up.

[0082] Further enhanced yields and / or product purity can be achieved by specific start-up strategies and / or specific stabilization concepts.

[0083] All pressures given are absolute. All ppm values ​​are by weight.

[0084] Examples of the invention are illustrated in the figures and further explained in the following description. [Brief explanation of the drawings]

[0085] [Figure 1] 1A-1C are cross-sectional views of towers with various intake pipe configurations. [Figure 2] 1A-1C are cross-sectional views of towers with various intake pipe configurations. [Figure 3] 1A-1C are cross-sectional views of towers with various intake pipe configurations. [Figure 4] 1A-1C are cross-sectional views of towers with various intake pipe configurations. [Figure 5] 1A-1C are cross-sectional views of towers with various intake pipe configurations. [Figure 6] A three-dimensional depiction of a tower with two intake pipes. [Figure 7] A three-dimensional representation of a tower with two intake pipes of different diameters. [Figure 8] FIG. 1 is a vertical cross-sectional view of a tower with an intake pipe. [Figure 9] 1 is a histogram showing relative velocities at the inlet of separation active internals in the form of packing. [Figure 10] 1 is a frequency function of the relative velocity at the inlet of separation active internals in the form of packing for different intake pipe configurations. [Figure 11] 10 is a frequency function of the relative velocity at the inlet of a separation active internal in the form of a tray for different intake pipe configurations. [Figure 12] 10 is a frequency function of the relative velocity at the inlet of a separation active internal in the form of a tray for different intake pipe configurations and non-uniform flow velocities in the intake pipe. [Figure 13] 10 is a frequency function of relative velocity at the inlet of separation active internals in the form of a tray for different intake pipe configurations and unequal intake pipe diameters. [Figure 14] It is a frequency function of the relative velocity in the single and double intake manifolds. [Figure 15] 1 is a schematic diagram of an apparatus for carrying out a mass transfer process. DETAILED DESCRIPTION OF THE INVENTION

[0086] 1 to 5 show cross-sections of towers 2 with various arrangements of intake pipes 3, 5.

[0087] In Figure 1, according to the prior art, the first intake pipe 3 and the second intake pipe 5 are arranged on the tower 2 at an angle α of 180°. Furthermore, the intake pipes 3, 5 are oriented in a radial direction 4 on the tower 2.

[0088] The tower 2 shown in Figures 2 and 3 also has exactly two intake pipes 3, 5. In this case, the angle α between the two intake pipes 3, 5 is less than 180°. In Figure 2, the angle α is 90°, and in Figure 3, the angle α is 120°. Another angle β between the two intake pipes 3, 5 is 270° in Figure 2 and 240° in Figure 3. The two intake pipes 3, 5 therefore have inequalities relative to each other due to their unequal distribution on the periphery 19 of the tower 2, resulting in circumferential sections with different lengths being formed between the intake pipes 3, 5.

[0089] In Figure 4, three intake pipes 3, 5, 25 for introducing the gas phase are arranged on the tower 2. The angle α between the intake pipes 3, 5, 25 is in each case 120°, and the intake pipes 3, 5 are evenly distributed on the circumference 19. This is up to this point an embodiment according to the prior art, since there are equal intake pipe diameters 6, 17 and equal velocities in the intake pipes 3, 5, 25. In the case of at least two different intake pipe diameters 6, 17 and / or at least two different velocities through the intake pipes 3, 5, 25 arranged as shown, an embodiment of the invention exists.

[0090] 5 shows a tower 2 with four intake pipes 3, 5, 25, 27. These intake pipes are evenly distributed around the circumference 19 of the tower 2, and the angle α between the intake pipes 3, 5, 25, 27 is 90° in each case. This is similar to prior art embodiments so far, since there are equal intake pipe diameters 6, 17 and equal velocities in the intake pipes 3, 5, 25, 27. Embodiments of the present invention exist for at least two different intake pipe diameters 6, 17 and / or at least two different velocities through the intake pipes 3, 5, 25, 27 arranged as shown.

[0091] Figure 6 is a three-dimensional representation of a tower 2 with two intake pipes 3, 5. To provide a better overview, only the area of ​​the tower 2 where the intake pipes 3, 5 are located is shown.

[0092] Two intake pipes 3, 5 for introducing the gas phase are arranged on the tower 2. The intake pipes 3, 5 are arranged at an angle α between 60° and 150° relative to each other. In the embodiment shown herein, the angle α is 90°. In particular, in the arrangement of the intake pipes 3, 5, the intake pipes 3, 5 are not arranged opposite each other in a straight line. Furthermore, if three or more intake pipes 3, 5 are provided, it is advantageous for the angles between the intake pipes 3, 5 to be different. As a result, direct collision of the gas phase introduced through the intake pipes 3, 5 is avoided, thus achieving a more uniform flow distribution.

[0093] Above the intake pipes 3, 5 for introducing the gas phase, there are separation-active internals 9 in the form of packing in the column 2, having an inlet 11.

[0094] Figure 7 shows a three-dimensional representation of a tower 2 with two intake pipes 3, 5, which essentially corresponds to the tower 2 according to Figure 6, with the difference that in this case the intake pipes 3, 5 have different intake pipe diameters 6, 17. The first intake pipe 3 has a larger intake pipe diameter 6 than the other intake pipe diameter 17 of the second intake pipe 5.

[0095] 8 shows a vertical cross section of the column 2 according to FIG. 6, which has a column section 29 and intake pipes 3, 5. The column section 29 has a free cross-sectional area and a section height 28. The intake pipes 3, 5 have an intake pipe diameter 6 and are each located at a height 8 above the column 2, which has a column diameter 7. [Example]

[0096] <Example 1> The relative velocity distribution at the inlet 11 to the packing 9 of the column 2 was determined. The calculation was based on an arrangement of two intake pipes 3, 5 at the same height and arranged at an angle α of 120° to each other.

[0097] For the calculation of the vapor flow rates given herein, packing with a height of 1 m and a pressure drop of 1 mbar was assumed as the separation active internals 9. For the calculation, the column diameter 7 of the column 2 was assumed to be 3200 mm, and the inlet pipe diameter 6 of the two inlet pipes 3, 5 was assumed to be 1000 mm. The pressure in the column 2 was 5.5 bar and the gas density was 16.6 kg / m 3 , gas viscosity is 1.3 10 -5 The boundary conditions for calculating the velocities were set as follows: 1.07 m / s with an F coefficient of 4.34 in inlets 3 and 5, and 0.21 m / s with an F coefficient of 0.85 in tower 2. The F coefficient is related to the vapor throughput in tower 2 and is calculated by multiplying the average velocity of the gas phase (m / s) by the gas density (kg / m 3 ) multiplied by the square root of

[0098] Inside the column 2, a system is installed in which a number of spiral structures, not shown here, and in which flow paths, also not shown here, run upwards towards the separation active internals 9, i.e. the packing.

[0099] The vertical velocity component at the inlet 11 of the separation-active internal 9 is a measure of the misdistribution installed in the column 2 .

[0100] In order to be able to properly use the misdistribution as a measure of flow uniformity, it is useful to first plot the calculated vertical velocity at the inlet 11 of the column 2 in a histogram. Such a histogram is shown as an example in Figure 9.

[0101] To generate a histogram, for example, the vertical velocities at the inlet 11 to the separation active internals 9, calculated using a suitable simulation program for calculating flow rates, can be visually plotted on a gray scale and a histogram generated using shades of gray. For each velocity, the histogram shows the percentage of the cross-sectional area over which that velocity occurs. Here, velocity is plotted on the horizontal axis 21 and cross-sectional area is plotted on the vertical axis 23.

[0102] <Example 2> In each case, the cumulative frequency functions for different intake pipe layouts, intake pipe configurations, and operating modes, as shown in Figures 10-14, were calculated from the histogram data shown in Figure 9. The difference between the velocity magnitude where velocity is high over only 5% of the cross-sectional area and the velocity magnitude where velocity is low over only 5% of the cross-sectional area, is calculated as a measure of maldistribution. The smaller this difference, the more uniform the flow distribution.

[0103] Figure 10 shows the frequency function of relative velocity at the inlet 11 to the separation active internals 9, i.e., the charge, for different configurations of the intake pipes 3, 5. Here, velocity is plotted on the horizontal axis 31 and cumulative area fraction, ranging from 0 (no cumulative fraction) to 1 (total area), is plotted on the vertical axis 33.

[0104] In a first arrangement, the angle α between the intake pipes 3, 5 is 90°. A corresponding first curve of the frequency function is indicated by reference sign 35. A second curve 37 shows the frequency function for an arrangement of the intake pipes 3, 5 with an angle α of 120°, and a third curve 39 shows the frequency function for an arrangement of the intake pipes 3, 5 with an angle α of 180°.

[0105] Unlike the histograms in Figure 9, the velocities in Figure 10 were calculated for a column 2 with a column diameter 7 of 6400 mm. The intake pipe diameters 6, 17 were in all cases 3000 mm, the pressure was 0.025 bar, and the gas density was 0.118 kg / m 3 , gas viscosity is 7.8·10 -6 Other boundary conditions were set as follows: Pa·s, the velocities in intake pipes 3 and 5 were 11.7 m / s with an F coefficient of 4 in both cases, and the velocity in tower 2 was 5.46 m / s with an F coefficient of 1.87.

[0106] The intersections of curves 35, 37, 39 with a cumulative area fraction of 95% (41) represent velocities such that the velocity is greater in only 5% of the cross-sectional area, and the intersections of curves 35, 37, 39 with a cumulative area fraction of 5% (43) represent velocities such that the velocity is less in only 5% of the cross-sectional area. The difference can then be determined graphically in a simple manner. When all curves 35, 37, 39 shown in this specification are plotted graphically, the maldistribution can be read directly. In each case, the greater the distance between the intersection of a curve 35, 37, 39 with line 41 or 43, the greater the maldistribution. Therefore, in the two-intake pipe arrangement 3, 5, it can be seen that the greatest maldistribution occurs at an intake pipe angle α of 180°, and therefore a smaller angle α should be selected. The difference in maldistribution for inlet pipe placement at 90° or 120° is very small compared to maldistribution at 180°, because this exact angle of 180° can be adapted to the piping situation of the tower, for example.

[0107] <Example 3> Figure 11 shows the frequency distribution for a column 2 having a column diameter 7 of 2900 mm and in each case an inlet pipe diameter 6, 17 of the inlet pipes 3, 5 of 900 mm. The tray with a pressure drop of 3 mbar at the inlet 11 of the separation active internals 9, i.e. the lowest tray, was assumed as the separation active internals 9 in the column 2. The calculation was based on an arrangement of two inlet pipes 3, 5 at the same height and arranged in each case at an angle α of 60°, 90°, 120° or 180° to each other.

[0108] The pressure in column 2 is 1.2 bar and the gas density is 1.63 kg / m 3 , gas viscosity is 1.2·10 -5 The boundary conditions for the calculation of the velocities were set as follows: Pa·s, the velocities in the intake pipes 3 and 5 were 7.4 m / s with an F coefficient of 9.4 in both cases, and the velocity in the tower 2 was 1.82 m / s with an F coefficient of 1.43.

[0109] A system of multiple volutes, not shown here, and flow paths therein, also not shown here, running upwards towards the trays, is installed inside the column 2. The vertical velocity component at the inlet 11 to the lowest tray is a measure of the misdistribution installed in the column 2.

[0110] For each of the different intake pipe arrangements, a cumulative frequency function was calculated from histogram data (not shown in the figures) in a manner similar to that shown in FIG. 9, and is shown in FIG.

[0111] The difference between the velocity magnitude where only 5% of the cross-sectional area is high and the velocity magnitude where only 5% of the cross-sectional area is low is calculated as a measure of maldistribution. The smaller this difference, the more uniform the flow distribution.

[0112] Figure 11 shows the frequency function of relative velocity at the inlet 11 to the separation active internals 9, i.e. to the tray, for different intake pipe arrangements, where velocity (m / s) is plotted on the horizontal axis 31 and cumulative area fraction from 0 (no cumulative fraction) to 1 (total area) is plotted on the vertical axis 33.

[0113] In a first arrangement, the angle α between the intake pipes 3, 5 is 60°. An associated fourth curve (dashed line) of the power function is indicated by reference symbol 44. A second curve 45 (solid line) shows the power function for an arrangement of the intake pipes 3, 5 at an angle α of 90° to one another, a third curve 46 (dotted line) shows the power function for an arrangement of the intake pipes 3, 5 at an angle α of 120° and a fourth curve 47 (dashed line) shows the power function for an arrangement of the intake pipes 3, 5 at an angle α of 180°.

[0114] The intersections of curves 44, 45, 46, and 47 with a cumulative area ratio of 0.95 (41) represent velocities of magnitude greater than the velocity in only 5 parts of 100 of the cross-sectional area. The intersections of curves 44, 45, 46, and 47 with a cumulative area ratio of 0.05 (43) represent velocities of magnitude less than the velocity in only 5 parts of 100 of the cross-sectional area. The difference can then be determined graphically in a straightforward manner. When all curves 44, 45, 46, and 47 are plotted on a graph, as shown here, the maldistribution can be read directly. In each case, the greater the distance between the intersections of a single curve 44, 45, 46, or 47 with line 41 or 43, the greater the maldistribution. Therefore, for a two-intake pipe arrangement (3, 5), the maximum maldistribution occurs at an intake pipe angle α of 180°, as shown here. The results shown in Figure 11 are summarized in Table 1.

[0115] [Table 1]

[0116] <Example 4> Figure 12 shows the frequency distribution of tower 2, which essentially corresponds to tower 2 of example 3. Here, different velocities prevail in the two intake pipes 3, 5, each with an intake pipe diameter 6, 17 of 900 mm.

[0117] In the first intake manifold 3, a velocity of 8.9 m / s with an F-factor of 11.3 and in the second intake manifold 5, a velocity of 5.9 m / s with an F-factor of 7.5 were used as the basis for the calculation.

[0118] FIG. 12 shows, in a manner corresponding to FIG. 11, the frequency function of the relative velocity at the inlet 11 to the separating active internals 9 for different intake pipe arrangements, here with different gas flow velocities prevailing in the intake pipes 3, 5.

[0119] In a first arrangement, the angle α between the intake pipes 3, 5 is 60°. An associated eighth curve (dashed-dotted line) of the power function is indicated by reference numeral 60. A ninth curve 62 (solid line) shows the power function for an arrangement of the intake pipes 3, 5 at an angle α of 90° to one another, while a tenth curve 64 (dotted line) shows the power function for an arrangement of the intake pipes 3, 5 at an angle α of 120° and an eleventh curve 66 (dashed line) shows the power function for an arrangement of the intake pipes 3, 5 at an angle α of 180°.

[0120] The maximum maldistribution prevails at an angle α of 180° in the intake manifold, and the uniformity of distribution is further improved for other configurations compared to the embodiment with equal velocity (see Table 1). The results shown in Figure 12 are summarized in Table 2.

[0121] [Table 2]

[0122] <Example 5> Figure 13 shows the frequency distribution of tower 2, which essentially corresponds to tower 2 of Example 3. Here, two intake pipes 3, 5 having different intake pipe diameters 6, 17 are present with a gas flow velocity in intake pipes 3, 5 each being 7.4 m / s with an F-factor of 9.4.

[0123] The intake pipe diameter 6 of the first intake pipe 3 was set to 794 mm, and the other intake pipe diameter 17 of the second intake pipe 5 was set to 995 mm, which were used as the basis for the calculation.

[0124] FIG. 13 shows, in a manner corresponding to FIG. 11, the frequency function of the relative velocity at the inlet 11 of the separating active internals 9 for different intake pipe arrangements, here with intake pipes 3, 5 having different intake pipe diameters 6, 17.

[0125] In a first arrangement, the angle α between the intake pipes 3, 5 is 60°. An associated twelfth curve (dashed-dotted line) of the power function is indicated by reference numeral 68. A thirteenth curve 70 (solid line) shows the power function for an arrangement of the intake pipes 3, 5 at an angle α of 90° to one another, while a fourteenth curve 72 (dotted line) shows the power function for an arrangement of the intake pipes 3, 5 at an angle α of 120° and a fifteenth curve 74 (dashed line) shows the power function for an arrangement of the intake pipes 3, 5 at an angle α of 180°.

[0126] The greatest maldistribution prevails at an intake manifold angle α of 180°, with the distribution uniformity being further improved compared to the embodiment with equal intake manifold diameter (see Table 1). The results shown in Figure 13 are summarized in Table 3.

[0127] [Table 3]

[0128] <Example 6> As boundary conditions in Figure 14, the same conditions as those described in Figure 9 were chosen, except that the velocities in the intake pipes 3, 5 were increased by a factor of 1.5 and the intake pipe diameters 6, 17 were correspondingly reduced to obtain the same velocities in the tower.

[0129] In the curve 55 showing the frequency distribution for the two intake pipes 3 and 5, the angle α between the intake pipes 3 and 5 was set to 120°. 0.5 A double-larger diameter of the intake pipe 3 was used, so that the F-factor and velocity in the column 2, and therefore also the pressure drop in the separation active internals 9, i.e. the packing, remained constant compared to the introduction of the gas phase via two intake pipes 3, 5.

[0130] The normalized velocity is plotted on the horizontal axis 51 and the area ratio is now plotted on the vertical axis 53 .

[0131] A first curve 55 shows the frequency distribution of the two intake pipes 3, 5. A second curve 59 shows the frequency distribution of the single intake pipe 3.

[0132] From the comparison in FIG. 14 it can be clearly seen that in the case of the tower 2 with two intake pipes 3, 5 a better uniform distribution is achieved.

[0133] <Example 7> The effect of maldistribution of the vapor phase leaving the two evaporators was investigated using a thermodynamic simulation of the whole plant for the production of n-butyl acrylate, based on the cross-sectional area of ​​the column.

[0134] Thermodynamic simulations were carried out using the software Aspen Plus®. A model databank for modeling unit operations and also a material databank were imported for specific material properties implemented in the software. Mixture properties were calculated by the software based on various thermodynamic models of material data of pure substances.

[0135] <Example 7a> To determine the energy consumption for a uniformly distributed gas phase, three vapor streams 15a, 15b, 15c with the same volume, as shown in FIG. 15, were used as a reference.

[0136] In the simulation, column 2 is shown as a fractionator 40 having three identical subcolumns 2A, 2B, and 2C, each of which was simulated using 13 theoretical plates.

[0137] At the top of the subcolumns 2A, 2B, 2C, the runback 16 in the form of a liquid phase was split into three equal volume liquid streams 16a, 16b, 16c and distributed over the three subcolumns 2A, 2B, 2C.

[0138] At the bottom of the column, the bottoms discharge streams 12a, 12b, 12c and the liquid streams 14c, 14d leaving the evaporators 20, 30 were combined to form overall stream 12, i.e., the liquid phase from column 2, which was mixed with feed stream 10. A small side stream 18 of overall stream 12 was discharged from the plant, and a main stream 13 of overall stream 12 was split into two equal volume streams 13a, 13b and fed to the two evaporators 20, 30.

[0139] Vapor streams 14a, 14b leaving evaporators 20, 30 and fed to column 2, for example, through inlets 3, 5, were combined to form vapor feed stream 15. Three equal volume streams 15a, 15b, 15c were then split in their respective vapor phases and introduced into three subcolumns 2A, 2B, 2C.

[0140] The splitting of the steam feed stream 15 was carried out uniformly in each case based on the steam feed stream 15: Steam stream (15a) 33.33 wt.%, Vapor stream (15b) 33.33 wt.%, Steam flow (15c) 33.33 wt%.

[0141] Thermodynamic simulation of the entire plant showed the following heat requirements in the evaporators 20, 30: Evaporator 20: 8922 kW, Evaporator 30: 8922 kW.

[0142] <Example 7b> To determine the energy consumption for a heterogeneously divided gas phase, three heterogeneous vapor streams 15a, 15b, 15c according to Figure 15 were used as a reference. Otherwise, the procedure was the same as in Example 7a.

[0143] The maldistribution of the vapor streams 14a, 14b leaving the evaporators 20, 30 over the cross-sectional area of ​​the column 2, which is caused by an unfavorable positioning of the intake pipes 3, 5 on the periphery of the column, was simulated by vapor streams 15a, 15b, 15c of different volumes being fed to the subcolumns 2A, 2B, 2C.

[0144] The splitting of the steam feed stream 15 was carried out unevenly in each case based on the steam feed stream 15: Steam stream (15a) 31.33 wt.%, Vapor stream (15b) 33.33 wt.%, Steam flow (15c) 35.33 wt%.

[0145] All other conditions remained unchanged compared to Example 7a.

[0146] Thermodynamic simulation of the entire plant showed the following heat requirements in the evaporators 20, 30: Evaporator (20): 9237 kW, Evaporator (30): 9237 kW.

[0147] Compared to Example 7a, about 3.5% more energy was required in the two evaporators with non-uniform steam introduction.

[0148] The local ratio of liquid and vapor phases in the rectification column 40 was changed due to the maldistribution of the vapor phase feed. More energy was required to accomplish the same separation task in the rectification column 40 than in the case of a uniform distribution of the vapor phase in Example 7a.

[0149] Comparing Example 7a with Example 7b, taking into account Examples 1 to 6, shows that the energy consumption for the same separation performance is reduced by a uniform distribution of the gas phase over the cross-sectional area of ​​column 2, in particular rectification column 40. This uniform distribution of the gas phase is achieved by the configuration of the intake pipes 3, 5 according to the invention. [Explanation of symbols]

[0150] 1. Apparatus for carrying out mass transfer processes 2 towers 2A, 2B, 2C subcolumns 3 First intake pipe 4 Radial direction 5 Second intake pipe 6 Intake pipe diameter 7 Tower diameter 8 Height 9 Separation active internal structure 10 Feed stream 11 Entrance 12 Overall flow, liquid phase 12a, 12b, 12c Bottoms discharge stream 13 Mainstream 13a, 13b Main stream 14a, 14b Outgoing steam flow 14c, 14d Outgoing liquid flow 15 Steam Feed Stream 15a, 15b, 15c Steam feed stream steam flow 16 Running Back 16a, 16b, 16c liquid flow 17 Other intake pipe diameters 18 Sidestream 19 Outer perimeter 20 First evaporator 21 Horizontal axis, speed 23 Vertical axis, cross-sectional area 25 Third intake pipe 27 Fourth intake pipe 28 section height 29 Tower Section 30 Second evaporator 31 Horizontal axis, relative velocity 33 Vertical axis, cumulative area ratio 35 First degree function curve 37 Second degree function curve 39 Third degree function curve 40 Rectification tower 41 95% cumulative area ratio 43 5% cumulative area ratio 44 Fourth degree function curve 45 Fifth degree function curve 46 Sixth degree function curve 47 Seventh Degree Function Curve 51 Horizontal axis, normalized velocity 53 Vertical axis, cumulative ratio by area 55 First frequency distribution curve 59 Second frequency distribution curve 60 Eighth Degree Function Curve 62 9th degree function curve 64 Tenth degree function curve 66 11th degree function curve 68 12th degree function curve 70 13th degree function curve 72 14th degree function curve 74 15th Degree Function Curve α angle β Other angles

Claims

1. An apparatus (1) for carrying out a mass transfer process, comprising a column (2) having at least two intake pipes (3, 5) for introducing a gas phase, a separation active internal (9) is housed in the tower (2), a tower section (29) extends from the at least two intake pipes (3, 5) to the separation active internal (9), the tower section (29) may or may not include internals, and if the tower section (29) includes internals, the occupancy of the cross-sectional area of ​​the tower (2) by the internals in the tower section (29) is less than 25% based on the total cross-sectional area; The at least two intake pipes (3, 5) have a height offset (here, the height offset refers to the distance in the height direction of the intake pipes from the center position of the cross section of each intake pipe) that is equal to or less than three times the largest intake pipe diameter (6) of the diameters of the intake pipes, the at least two intake pipes (3, 5) have an angle (α) between their central axes that is 60° to 150°, and the at least two intake pipes (3, 5) have different intake pipe diameters (6, 17).

2. The device (1) described in claim 1, wherein the at least two intake pipes (3, 5) are arranged asymmetrically on the outer periphery (19) of the tower (2).

3. 3. The device (1) according to claim 1 or 2, wherein said angle (α) differs from the other angle β between two of said at least two intake pipes (3, 5) by at least 10°.

4. 4. The device (1) according to any one of claims 1 to 3, wherein the at least two intake pipes (3, 5) are arranged at the same height (8) above the tower (2).

5. 5. The device (1) according to any one of claims 1 to 4, wherein the at least two intake pipes (3, 5) are arranged at the bottom of the column (2) or as side intakes on the column (2).

6. 6. The device (1) according to claim 1, wherein the device (1) comprises exactly two intake pipes (3, 5) for introducing a gas phase, the two intake pipes (3, 5) having a height offset corresponding to no more than three times the diameter of the largest of the intake pipe diameters (6).

7. 7. The device (1) according to any one of claims 1 to 6, wherein the at least two intake pipes (3, 5) are arranged so that their central axes are radially arranged from the center of the tower (2), and each intake pipe opens into the tower (2).

8. 8. The apparatus (1) according to any one of claims 1 to 7, wherein the separation active internals (9) comprise structured packing and / or packing components.

9. 9. The apparatus (1) according to any one of claims 1 to 8, wherein the separation active internals (9) comprise dual flow trays, ripple trays and / or cascade trays.

10. 9. The apparatus (1) according to any one of claims 1 to 8, wherein the separation active internals (9) comprise cross-flow trays.

11. 11. The device (1) according to any one of claims 1 to 10, wherein an evaporator (20, 30) is attached to the tower (2) via the at least two intake pipes (3, 5).

12. 12. Use of the apparatus (1) for carrying out the mass transfer process according to any one of claims 1 to 11 for isocyanate, styrene or alkyl acrylate production or in a cracking unit.

13. Use of an apparatus (1) for carrying out a mass transfer process as described in claim 12, wherein the flow rates through the at least two intake pipes (3, 5) are different from each other.

14. The device (1) for carrying out the mass transfer process is ２ 14. Use according to claim 12 or 13, in which the butyl acrylate is used as a rectification column (40) in a process for the continuous production of C═CH—C(═O)OR, where R=n-butyl or isobutyl, in which aqueous 3-hydroxypropionic acid is reacted in the presence of a suitable butanol (R—OH) under dehydration and esterification conditions in a reactor comprising said rectification column (40), the butyl acrylate formed, the unreacted butanol, and further water used and water formed being distilled at the top of the column as a ternary azeotrope, and after separation into a liquid aqueous phase and a liquid organic phase, respectively, the aqueous phase and the organic phase, respectively, are at least partially discharged, and the organic phase comprising the butyl acrylate and the butanol is fractionally distilled.

15. 15. Use according to claim 14, wherein a liquid phase (12) is withdrawn from the rectification column (40), at least partially vaporized and at least partially recycled to the rectification column (40) via the at least two intake pipes (3, 5).

16. 16. Use according to claim 15, wherein the liquid phase (12) is at least partially vaporized in at least two evaporators (20, 30).

17. 17. Use according to any one of claims 14 to 16, wherein the pressure at the top of the rectification column (40) is in the range of 0.2 bar absolute to 5.0 bar absolute.

18. The use according to any one of claims 14 to 17, wherein the fractional distillation of the organic phase comprising butyl acrylate and butanol is carried out by distilling the butanol in an additional fractionator (40) and distilling butyl acrylate from the bottom liquid thus obtained in another additional fractionator (40').

19. A method for designing an apparatus (1) for mass transfer according to any one of claims 1 to 11, comprising the following steps: (a) determining the position and orientation of said at least two intake pipes (3, 5) on said tower (2); (b) calculating gas flow in said column (2) using flow simulation; (c) repeating steps (a) and (b) using different positions and orientations of the at least two intake pipes (3, 5); (d) selecting the position and orientation of the at least two intake pipes (3, 5) that exhibit the most uniform flow pattern calculated in step (c).

Images